This application is based on Patent Application No. 10-092119 filed Apr. 3, 1998 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a printing apparatus and a head driving method thereof, and particularly relates to a printing apparatus of serial scan type having a plurality of printing heads, each having a plurality of in-line-arranged printing elements and a head driving method thereof.
2. Description of the Related Art
Conventionally, a printing apparatus of a serial scan type is used, at an office or at home, for producing printouts of high quality color images. The serial scan type printing apparatus performs printing on a sheet-formed printing medium by a reciprocal printing head movement (henceforth referred to as main scanning), and carrying the printing medium by a prescribed amount per main scanning, in a direction substantially vertical to the reciprocal movement (henceforth referred to as sub-scanning), repeatedly. A configuration, with a plurality of printing heads to which multiple types of printing liquids (inks) are distributed for printing, is the mainstream in this type of printing apparatus that prints out color images.
In such a printing apparatus that performs main scanning employing with a plurality of printing heads, its image quality is lowered with a formed-position (registration) offset among printed pixels by each printing head. A registration offset is mostly ascribed to the molding precision or assembling accuracy of members in the printing apparatus. The current serial scan type printing apparatuses mostly achieves such high definition of printing resolution with 360 dpi or more, that it has become difficult to reduce the registration offset with an improvement in the mechanical precision of scanning systems.
Thus, as registration methods, methods of controlling a timing of forming printed dots (pixels), for adjustment, are adopted.
Generally, these registration methods can be classified into two types to be adopted.
One is to adjust registration by designing for driving each printing head at an independent timing and setting each drive timing independently. The other is to adjust registration by delaying a timing of forming printed pixels for every pixel.
However, the former registration method has a considerable demerit in cost, since pulse generating means for generating drive pulses at an independent timing for each head and transfer means for transferring drive data at an independent timing, as well as timing controlling means for controlling short time intervals, must be provided with.
Also, the latter registration method occurs, as done only by every pixel, a registration offset of at most a half of printed pixel width.
An object of the present invention is to provide a printing apparatus that improves the precision of registration, twice of or larger than a printing resolution, and a head driving method thereof, in terms of a serial scan type printing apparatus that generates drive pulses of an equal timing to a plurality of printing heads and transfers drive data at an equal timing, and a head driving method thereof.
Another object of the present invention is to provide a printing apparatus and a printing method which can detect a printing position offset between printing heads in a main scanning direction on a printing medium and can set, if the detected offset amount is larger than a prescribed value, an in-block driving sequence independently for each printing head to correct the printing position offset.
A printing apparatus according to the present invention comprises scanning means for relatively moving a plurality of printing heads having a plurality of recording elements and a printing medium in a prescribed direction, driving means for driving the plurality of recording elements of each printing head while dividing them into a plurality of blocks, wherein each recording element in each block is driven in a prescribed sequence during the relative movement, and correcting means, responsive to a print position offset between the plurality of printing heads in the prescribed direction on the printing medium, for setting the in-block driving sequence independently for each printing head to correct the print position offset.
A head driving method of a printing apparatus according to the present invention includes the steps of relatively moving a plurality of printing heads having a plurality of recording elements and a printing medium in a prescribed direction, of dividing the plurality of recording elements of each printing head into a plurality of blocks, and of driving each recording element in each block in a prescribed sequence during the relative movement, and the method further comprises the steps of detecting an amount of print position offset between the plurality of printing heads in the prescribed direction on the printing medium, and of correcting the print position offset by setting the in-block driving sequence independently for the each printing head according to the detected offset amount.
In the apparatus and the method according to the present invention, a printing position offset between printing heads in a main scanning direction on a printing medium can be detected, and if the detected offset amount is larger than a prescribed value, an in-block driving sequence is set independently for each printing head to correct the printing position offset. Thereby, accuracy of printing position adjustment between printing heads in the main scanning direction can be increased, and then correcting a registration offset with accuracy can achieve a high quality image.
It should be noted that throughout the description and claims the wording xe2x80x9cprintingxe2x80x9d means, in broad sense, not only forming significant information such as characters or graphics but also forming images, figures, patterns and the like on the printing medium or processing the medium irrespective of whether the information is significant or not and whether the information is overt or not in such a manner as to be visually perceived by a person.
Here, the wording xe2x80x9ca printing mediumxe2x80x9d means, in broad sense, not only paper to be typically used in the printing apparatus but also cloths, plastic films, metal plates and the like which can receive the ink.
Furthermore, the wording xe2x80x9cinkxe2x80x9d should be understood in broad sense similarly to the definition of xe2x80x9cprinting,xe2x80x9d and should include any liquid to be used for formation of images, figures, patterns and the like or for processing of the printing medium by applying the ink to the printing medium.
Throughout the description and claims, the optical characteristics include the optical density, namely, the reflection optical density using a reflection index and the transmission optical density using transmittance. But, an optical reflection index, the intensity of reflected light or the like may be used. In the following description and claims, the reflection optical density is mainly used as the optical characteristics and is simply referred to as the optical density or the density without any particular confusion.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.